1. Field of the Invention
The present invention relates to wireless communications and, more particularly, to management of dropped calls in a wireless communication system.
2. Description of Related Art
Cellular wireless, like other forms of wireless communication, is an increasingly popular means of personal communication in the modem world. People are using cellular wireless networks for the exchange of voice and data over cellular telephones, Personal Digital Assistants (“PDAs”), cellular telephone modems, and other devices. In principle, a user can seek information over the Internet or call anyone over a Public Switched Telephone Network (“PSTN”) from any place inside the coverage area of the cellular wireless network.
In a typical cellular wireless system, an area is divided geographically into a number of cell sites, each defined by a radio frequency (“RF”) radiation pattern from a respective base transceiver station (“BTS”) antenna. Each BTS antenna in a cell is in turn coupled with a base station controller (“BSC”), cooperatively defining a base station system. And the BSC is then coupled to or functionally integrated within a switch (e.g., a mobile switching center (“MSC”)) and/or gateway (e.g., a packet data serving node (“PDSN”)) that provides connectivity with a transport network such as the PSTN (public switched telephone network) or a public or private IP network (e.g., the Internet).
When a mobile station, such as a cellular telephone, pager, or appropriately equipped portable computer, for instance, is positioned in a cell, the mobile station communicates via an RF air interface with the BTS antenna of the cell. Consequently, a communication can be established between the mobile station and another entity on the transport network, via the air interface, the BTS, the BSC and the switch or gateway. Such a communication may be referred to as a “call,” whether the communication is a traditional voice “call” or a more advanced data session.
Communications between the mobile station and the BTS will typically suffer from varying levels of interference and signal degradation, due to factors such as (i) the number and power level of mobile stations concurrently communicating over the air interface, (ii) obstructions such as buildings, land or foliage, and (iii) the distance between the mobile station and the BTS. Consequently, the strength of RF signals that the mobile station receives from the BTS can vary. And the strength of RF signals that the BTS receives from the mobile station can vary.
When a mobile station is actively engaged in a call, if the RF signal strength received by the mobile station and/or BTS becomes too low, the RF link will be effectively cut off, which will thereby disconnect or “drop” the call.